Composition and process for imparting a bright blue color to zinc/aluminum alloy

ABSTRACT

The rapid, low-temperature formation of a bright blue surface on hot-dip zinc/aluminum alloy-plated steel sheet that contains 0.1 to 60 weight % aluminum in the alloy, or on other surfaces of similar chemical composition, using conventional surface-treatment equipment, is achieved by treating the surface with a treatment bath that has a pH of 3.5 to 6.0 and that contains molybdenum compound at 0.2 to 3.0 weight % as molybdenum and simple or complex fluoride at 0.1 to 2.0 weight % as fluorine.

TECHNICAL FIELD

The present invention relates to a treatment process for imparting ablue color to the surface of zinc aluminum alloys, particularly thehot-dip Zn/Al alloy-plated steel sheet that is widely used as aconstruction material and for household electrical appliances, withoutat the same time impairing the bright surface appearance (metallicluster or gloss) that is possessed by such plated steel sheet. (Theinvention will often be described below with respect to plated steelsheet, but it should be understood that most of this discussion appliesequally well to any other surface with the same chemical nature.) Morespecifically, the present invention relates to a novel composition andprocess for imparting a bright or brilliant blue color to hot-dip Zn/Alalloy-plated steel sheet, wherein the treatment bath in said process isvery stable and the process can be run in simple equipment using lowertemperatures and shorter times than in prior methods.

BACKGROUND ART

Metal coloring methods generally consist of inorganic chemical methods,organic chemical methods, electrolytic methods, and painting. Amongthese, the inorganic chemical coloring methods are the most advantageousin terms of equipment, cost, and workability. However, while variousinorganic chemical coloring methods have been devised for application toaluminum sheet, aluminum alloy sheet, and zinc-plated steel sheet, aninorganic chemical coloring process has yet to be established forapplication to hot-dip zinc/aluminum alloy-plated steel sheet.

In specific terms, the following methods are known for the inorganicchemical coloring of aluminum and aluminum alloy:

(1) The generation of a deep black color by treatment at 80° C. for 10minutes with an aqueous solution of 10 to 20 g/L of ammonium molybdateand 5 to 15 g/L of ammonium chloride;

(2) The generation of a brilliant sudan color by treatment for 5 minutesat 50° C. to 70° C. with an aqueous solution of 8 g/L of zinc sulfate,3.3 g/L of sodium molybdate, and 2 g/L of sodium fluoride; and

(3) The formation of a protective film on the surface of aluminiferousmaterial using a composition that contains hexavalent chromium, fluorideion, and a compound selected from molybdic acid and its sodium,potassium, and ammonium salts (Japanese Patent Publication Number Sho45-32922 32,922/1970!).

Treatment methods (1) and (2) are described by Takakado Nakayama in TheSurface Treatment of Aluminum Aruminiumu no Hycomen Shod! (Nikkan KogyoShinbun-sha, 1969).

Various coloring methods for zinc-plated steel sheet have also beenexamined, and, as for aluminum and aluminum alloy, the inorganicchemical coloring methods offer advantages in terms of equipment, cost,and workability and are therefore in wide use. With regard to theinorganic chemical coloring of zinc-plated steel sheet, for example,Japanese Patent Application Laid Open Kokai! Number Sho 61-253381253,381/1986!) discloses

(4) a method for blackening zinc-plated steel sheet using an aqueoussolution that contains copper ion and nickel ion.

In addition, the prior art for the coloration of zinciferous-platedsteel sheet primarily yields blacks and browns, and a blue color andparticularly a bright blue with a metallic gloss have heretofore beenunavailable.

The application of prior-art methods (1) to (4) as described above tohot-dip zinc/aluminum alloy-plated steel sheet will now be considered.In the case of treatment methods (1) and (2), their application tohot-dip zinc/aluminum alloy-plated steel sheet does not produce thecolors obtained by their application to aluminum or aluminum alloy, andin fact almost no change in color is obtained in either case. Moreover,since these treatments are intended principally for application tomoldings, they require lengthy treatment times of at least 5 minutes.Because the treatment bath used in treatment method (3) is essentially achromate treatment bath, the precipitated coating consists of a chromatefilm whose principal component is chromium oxide and which is thereforeyellowish. Moreover, when the pH is increased to 3.5 to 6 in thismethod, the reactivity is diminished, the chromate coating weighttherefore declines, and coloration does not occur. While treatmentmethod (4) does rapidly produce a matte black appearance, this blackcoating is weakly adhesive, and the execution of some type ofpost-treatment is required as a result in order to improve itsadherence.

In short, it has been determined that the rapid generation of a brightblue appearance cannot be obtained through the application to hot-dipzinc/aluminum alloy-plated steel sheet of a prior coloring methodintended for aluminum, aluminum alloy, or zinc-plated steel sheet.

Hot-dip zinc/aluminum alloy-plated steel sheet is widely used at presentas a construction material and for household electrical appliances. Itssurface has a white metallic luster. Although an elegant look isprovided by the metallic luster, the appearance of this material isultimately aesthetically unsatisfactory because it lacks a sense ofcalmness and quality. Accordingly, there is strong demand for theappearance of a surface-treatment technology for hot-dip zinc/aluminumalloy-plated steel sheet that will yield a bright blue color which doesnot clash with but rather is in harmony with its surroundings and whichalso combines an elegant look with a high metallic luster.

DISCLOSURE OF THE INVENTION Problems to Be Solved by the Invention

Specifically, the present invention seeks to introduce a method forimparting a bright blue color to the surface of hot-dip zinc/aluminumalloy-plated steel sheet, wherein said method employs the inorganicchemical coloring approach and does not require large-scale equipment,accomplishes this blue coloring faster and at lower temperatures than inprevious coloring methods, and does not impair the original metallicluster of hot-dip zinc/aluminum alloy-plated steel sheet.

SUMMARY OF THE INVENTION

The inventors proceeded with their investigations after concluding thatan elucidation of the following two points would be critical to aresolution of the problems described above for the prior art:

1. the nature of the constituent components of a film having the desiredblue color, and

2. the chemical reactivity between the components of the treatment bathand hot-dip zinc/aluminum alloy-plated steel sheet.

It was discovered, first, that molybdenum compounds are the optimaltreatment bath components for inducing the formation of a blue film onhot-dip zinc/aluminum alloy-plated steel sheet and that achieving thedesired colored film using other inorganic compounds is quiteproblematic.

It was also discovered that the treatment bath preferably contains aparticular quantity of fluoride in order to remove the tough oxidationcoating present on the surface of hot-dip zinc/aluminum alloy-platedsteel sheet and in order to provide a rapid etch of the plating layer.Furthermore, as the result of investigations into the relationshipbetween pH and the etching reactivity of fluorides, it was determinedthat these compounds are not active throughout the entire pH range andthat only at pH 3.5 to 6 is the reaction rate optimal for the coloringtreatment that is the objective of the invention. The inventorsdiscovered that only under this condition is it normally possible toobtain a uniform etch that does not impair the metallic luster. Thepresent invention was achieved based on these discoveries.

In specific terms, the process in accordance with the present inventionfor imparting a bright or brilliant blue color to zinc/aluminum alloysurfaces that contains 0.1 to 60 weight % of aluminum, particularlythose of hot-dip zinc/aluminum alloy-plated steel sheet,characteristically comprises treatment of the surface with a treatmentbath that has a pH of 3.5 to 6, that does not contain chromium, and thatcomprises, preferably consists essentially of, or still more preferablyconsists of water, a molybdenum compound content of 0.2 to 3.0 weight %calculated as molybdenum, and a fluoride content of 0.1 to 2.0 weightcalculated as fluorine.

DESCRIPTION OF PREFERRED EMBODIMENTS

An aluminum content of 0.1 to 60 weight % is required in thezinc/aluminum alloy to which the process of the present invention isapplied. The desired bright blue color is not obtained when the aluminumcontent does not fall within this given range. Thus, when the aluminumcontent is below 0.1 weight %, the color darkens and the luster is lost.When the aluminum content exceeds 60 weight %, the coloring reactiondoes not develop to a satisfactory degree and the color, as a result,remains almost unchanged.

The molybdenum compound content in the treatment bath is preferably 0.2to 3.0 weight % as molybdenum and is obtained by the addition of solublemolybdenum compounds. The rate of the coloring reaction declines atbelow 0.2 weight %, while the use of more than 3.0 weight % iseconomically unattractive because the activity becomes saturated and nolonger improves. The particularly preferred molybdenum content is 0.5 to2.0 weight %. Operable soluble molybdenum compounds are molybdate salts,phosphomolybdic acid, molybdenum chloride, and the like.

The treatment bath preferably contains fluoride at 0.1 to 2.0 weight %as fluorine. The etching reaction rate declines and the coloringreaction rate therefore declines at below 0.1 weight %. The use of morethan 2.0 weight % is economically unattractive due to the absence ofadditional effects at such levels. A more preferred fluoride content is0.3 to 1.0 weight %. Operable fluoride sources are specificallyexemplified by hydrofluoric acid, sodium fluoride, potassium fluoride,ammonium fluoride, sodium bifluoride, fluosilicic acid, sodiumfluosilicate, ammonium fluosilicate, fiuoboric acid, fluotitanic acid,and fiuozirconic acid.

The pH of the treatment bath must be adjusted or regulated to 3.5 to 6.The etching reactivity of the fluorine in the fluoride etchant is toostrong at a pH below 3.5. This has the adverse result of reducing theamount of colored coating that is deposited and thus prevents theappearance of the desired color. In contrast to this, the etchingreactivity declines at a pH above 6, which leads to a sharp decline inthe rate of the coloring reaction. The pH can be regulated through theuse of an alkali such as sodium hydroxide, sodium carbonate, ammonia,ammonium bicarbonate, potassium hydroxide, and the like, or through theuse of an acid such as sulfuric acid, nitric acid, phosphoric acid, andthe like. The pH range of 3.8 to 4.5 is particularly preferred. Thetreatment bath used in the present invention does not require theaddition of chromic acid, chromium compounds, etc., and instead allchromium compounds are preferably omitted.

The above-described treatment bath is preferably applied to hot-dipzinc/aluminum alloy-plated steel sheet by spraying or immersion at atreatment temperature of 30° C. to 70° C. for a treatment time of 1 to10 seconds. The reactivity of the treatment bath is inadequate attreatment temperatures below 30° C., while treatment temperatures above70° C. do not afford any further increase in reactivity and aretherefore economically unattractive. The treatment temperature range of45° C. to 60° C. is particularly preferred. Treatment times less than 1second do not yield the desired coloration due to an inadequatereaction. The coloring reaction is saturated at treatment times inexcess of 10 seconds, and such treatment times therefore do not yieldany further change in color. Treatment times in the range of 2 to 5seconds are particularly preferred.

When the hot-dip zinc/aluminum alloy-plated steel sheet is contaminatedwith adhering oil, dirt, etc., it is preferably subjected to adegreasing process, for example, an alkali or solvent degreasingprocess, prior to execution of treatment in accordance with the presentinvention. Moreover, washing with water and drying after film formationmay be conducted in the present invention on an optional basis.

The effect of the present invention is in no way diminished by theexecution--after film deposition in accordance with the presentinvention--of a post-treatment (such as a chromate treatment, etc.) forthe purpose of enhancing the corrosion resistance of the hot-dipzinc/aluminum alloy-plated steel sheet.

The discussion will now turn to what is believed to be the reactionmechanism during treatment of hot-dip zinc/aluminum alloy-plated steelsheet by the treatment bath in accordance with the present invention,but these statements are not to be construed as limiting the invention.When zinc/aluminum alloy is treated with the treatment bath inaccordance with the present invention, the subject alloy surface isfirst etched due to the activity of the fluorine in the fluoride presentin the treatment bath. This etching reaction is extremely importantsince it determines the reaction rate of the colored film-formingreaction. The etching activity of the fluorine in the fluoride presentin the treatment bath undergoes major variations as a function oftreatment bath pH, and the optimal etching reactivity is maintained inthe pH range of 3.5 to 6. With regard to the tough oxidation filmspontaneously present on the surface of this type of plating layer, onlyin the optimal pH range is it efficiently dissolved and removed by thefluorine component and the coloring reaction thereby promoted. Moreover,the metallic luster characteristic of hot-dip zinc/aluminum alloy-platedsteel sheet is not impaired because the etching reaction in theinvention treatment proceeds uniformly against the subject platinglayer.

In addition, the zinc ion and aluminum ion eluted by the etchingreaction are believed to reprecipitate onto the surface of the platinglayer as hydrated oxides. Accompanying the elution, i.e., the oxidation,of the aluminum and zinc in the plated steel sheet under consideration,the molybdenum compound dissolved in the treatment bath is reduced to acompound with a lower oxidation number and precipitates onto the surfaceof the plating.

Thus, treatment of hot-dip zinc/aluminum alloy-plated steel sheet by thetreatment bath of the present invention is believed to cause thedevelopment of a bright blue color because a coating consisting of acomposite of molybdenum oxide and hydrated oxides of zinc and aluminumis formed on the surface of the plating layer, and the plating layerretains its metallic luster.

Any chromium component added to the treatment bath of the presentinvention, e.g., chromic acid, chromium compounds, and the like, acts asan inhibitor of the etching reaction and thus, if present in anysubstantial amount, prevents satisfactory development of the etchingreaction and thus renders precipitation of the colored film inadequate.Although the etching reaction can be accelerated in the presence ofchromium compounds by dropping the pH below 3.5, chromate filmprecipitation reactions then are believed to proceed in preference tomolybdenum oxide precipitation in this low pH region, and the yellowcolor of the chromate film is then produced rather than the blue causedby molybdenum oxide.

The invention can be further appreciated by consideration of thefollowing examples.

EXAMPLES AND COMPARISON EXAMPLES

1. Test materials

Six types of hot-dip zinc/aluminum alloy-plated steel sheet (platingmass=120 g/m²) were employed, and these were fabricated usingzinc/aluminum alloy plating baths. Six aluminum contents in the platinglayers were used: 0.05 weight %, 0.15 weight %, 5 weight %, 15 weight %,55 weight %, and 70 weight %. The aluminum content in the plating filmon the test sheet used in a particular example or comparison example isreported in the particular example (Examples 1 to 6) or comparisonexample (Comparison Examples 1 to 6).

2. The treatment process

The following treatment process steps were performed in each of theexamples and comparison examples. The individual conditions concerningthe coloring treatment itself are respectively reported in the examplesand comparison examples:

(1) Degreasing (FINECLEANER™ L4460, alkaline degreaser from NihonParkerizing Company, Limited) at 43° C. for 120 seconds by spraying.

(2) Water wash (tap water) at ambient temperature for 30 seconds byspraying.

(3) Coloring treatment as described below; the pH was adjusted withsodium hydroxide or sulfuric acid.

(4) Water wash (tap water) at ambient temperature for 30 seconds byspraying.

(5) Drying at 100° C. for 120 seconds.

Example 1

The test sheet (aluminum content in plating layer=5 weight %) wassprayed for 1 second with a treatment bath (pH=4.0, temperature=50° C.)that contained ammonium molybdate at 2.0 weight % as molybdenum andammonium bifluoride at 0.7 weight % as fluorine.

Example 2

The test sheet (aluminum content in plating layer=0.15 weight %) wasimmersed for 9 seconds in a treatment bath (pH=5.7, temperature=33° C.)that contained phosphomolybdic acid at 2.8 weight % as molybdenum,fluosilicic acid at 1.5 weight % as fluorine, and hydrofluoric acid at0.3 weight as fluorine (total fluorine=1.8 weight %).

Example 3

The test sheet (aluminum content in plating layer=55%) was immersed for3 seconds in a treatment bath (pH=3.6, temperature=67° C.) thatcontained sodium molybdate at 1.5 weight % as molybdenum andhydrofluoric acid at 0.5 weight % as fluorine.

Example 4

The test sheet (aluminum content in plating layer=0.15%) was sprayed for5 seconds with a treatment bath (pH=4.0, temperature=60° C.) thatcontained phosphomolybdic acid at 0.3 weight % as molybdenum and sodiumfluoride at 0.12 weight % as fluorine.

Example 5

The test sheet (aluminum content in plating layer=15%) was immersed for3 seconds in a treatment bath (pH=4.0, temperature=50° C.) thatcontained ammonium molybdate at 1.0 weight % as molybdenum andfluosilicic acid at 0.5 weight % as fluorine.

Example 6

The test sheet (aluminum content in plating layer=5 weight %) wasimmersed for 2 seconds in a treatment bath (pH=4.2, temperature=60° C.)that contained ammonium molybdate at 1.0 weight % as molybdenum andammonium fluoride at 0.7 weight % as fluorine.

Comparison Example 1

The test sheet (aluminum content in plating layer=70%) was immersed for0.7 seconds in a treatment bath (pH=5.5, temperature=27° C.) thatcontained ammonium molybdate at 1.5 weight % as molybdenum andfluosilicic acid at 0.5 weight % as fluorine.

Comparison Example 2

The test sheet (aluminum content in plating layer=0.05%) was immersedfor 10 seconds in a treatment bath (pH=3.3, temperature=70° C.) thatcontained phosphomolybdic acid at 1.0 weight % as molybdenum andhydrofluoric acid at 1.0 weight % as fluorine.

Comparison Example 3

The test sheet (aluminum content in plating layer=5%) was sprayed for 5seconds with a treatment bath (pH=3.0, temperature=50° C.) thatcontained ammonium molybdate at 1.0 weight % as molybdenum andhydrofluoric acid at 0.5 weight % as fluorine.

Comparison Example 4

The test sheet (aluminum content in plating layer=5%) was immersed for 5minutes in a treatment bath (temperature=60° C.) that contained 8 g/L ofzinc sulfate, 3.3 g/L of sodium molybdate (0.15 weight % as molybdenum),and 2 g/L of sodium fluoride (0.09 weight % as fluorine). The treatmentbath pH, which was not adjusted, was 6.2. This treatment corresponded toa treatment described in Takakado Nakayama, The Surface Treatment ofAluminum (Nikkan Kogyo Shinbun-sha, 1969) for imparting a brilliantsudan color to aluminum.

Comparison Example 5

The test sheet (aluminum content in plating layer=5%) was immersed for 2seconds in a treatment bath (pH=3.0, temperature=30° C.) that contained10 g/L of copper ions, 1.5 g/L of nickel ions, and 20 g/L potassiumchlorate. This treatment corresponds to the treatment method describedin Example 7 of Japanese Patent Application Laid Open Number Sho61-253381.

Comparison Example 6

The test sheet (aluminum content in plating layer=15%) was immersed for10 seconds in a treatment bath (temperature=50° C.) that contained 0.5weight % of chromium trioxide, 0.3 weight % of fluoride as HBF₄, andsodium molybdate at 0.1 weight % as molybdenum. The treatment bath pH,which was not adjusted, was 1.75. This treatment corresponds to thetreatment method described in Example 1 of Japanese Patent PublicationNumber Sho 45-32922.

Testing

The appearance of the test sheets processed in accordance with Examples1 to 6 and Comparison Examples 1 to 6 was determined using thetrichromatic specification symbols stipulated in JIS Z 8721. The gloss(60°) was measured prior to treatment (G1) and after treatment (G2), andthese values were used to calculate the gloss change ratio (DG=G2/G1).The adherence of the color film was evaluated based on the nature of itsdelamination when peeled with cellophane tape. These measurement resultsare reported in Table 1.

As Table 1 makes clear, a hue (2.5 B to 5 PB) centered on blue withsaturation≧3 was obtained by application of the coloring process inaccordance with the present invention to the surface of steel sheethot-dip plated with Zn/Al alloy that contained 0.1 to 60 weight % Al.Moreover, while coloration occurred to a lightness≦6, a gloss changeratio of at least 0.3 was maintained. In other words, these resultsconfirmed that treatment according to the present invention can impart ablue color with retention of the metallic gloss.

                  TABLE 1                                                         ______________________________________                                                  TCSS        Gloss                                                   Identifi-   Values        Ratio   Delami-                                     cation      Hue     L/S       Change                                                                              nation?                                   ______________________________________                                        Example 1   5     PB    4/6     0.32  No                                      Example 2   2.5   PB     5/10   0.41  No                                      Example 3   10    B     6/3     0.46  No                                      Example 4   2.5   B     5/4     0.35  No                                      Example 5   2.5   PB    5/8     0.40  No                                      Example 6   2.5   PB    5/6     0.44  No                                      Comparison  5     PB    9/1     0.63  No                                      Example 1                                                                     Comparison  2.5   B     9/2     0.21  No                                      Example 2                                                                     Comparison  5     P     8/2     0.08  No                                      Example 3                                                                     Comparison  5     B     8/1     0.13  No                                      Example 4                                                                     Comparison  5     R     2/1     0.01  Yes                                     Example 5                                                                     Comparison  2.5   Y      8/12   0.06  No                                      Example 6                                                                     ______________________________________                                         Notes for Table 1                                                             "TCSS" = Trichromatic Specification Symbol; "L/S" = Lightness/Saturation 

In contrast to this, in Comparison Example 1, the coloring reaction didnot develop to an adequate degree because the aluminum content in theplating layer exceeded 60 weight %. In Comparison Example 2, thehydrofluoric acid etching reaction was too strong because the bath pHwas below 3.5 and the plating layer contained less than 0.1 weight %aluminum. This inhibited the precipitation of the color film and alsocaused a decline in the gloss. In Comparison Example 3, the fluorineetching reaction was again too strong because the bath pH was a low 3.0.This inhibited the precipitation of the color film and destroyed themetallic luster. In Comparison Example 4, the bath pH exceeded 6.0 andthe bath contained soluble molybdenum compound at less than 0.2 weight %as molybdenum and fluoride at less than 0.1 weight % as fluorine. As aresult, the reactivity was inadequate, and the desired color could notbe obtained (as in Comparison Examples 1 and 2) despite a lengthytreatment time of 5 minutes. Comparison Example 5 was an example of theprior art for the blackening of zinciferous-plated materials. Thus,blackening was obtained in this case, but the luster was severelyreduced. Moreover, a satisfactory adherence was also not obtained. InComparison Example 6, the treatment bath contained chromic acid and hada low pH of 1.75. This resulted in the precipitation of a chromate film:Not only was a yellow color obtained, but the metallic luster was lost.

Benefits of the Invention

As discussed in the preceding, the process of the present invention forimparting a blue color to hot-dip zinc/aluminum alloy-plated steel sheetis a highly cost-effective inorganic chemical coloring process that iscapable of providing high added-value in terms of design and aesthetics.In addition, the treatment bath in the invention process is more stablethan prior treatment baths and treatment in accordance with theinvention process can be run at lower temperatures and in less time thanin prior processes.

The invention claim is:
 1. A process for imparting a bright blue colorto a zinc/aluminum alloy surface that contains 0.1 to 60 weight %aluminum by treatment of the surface with an aqueous liquid treatmentcomposition that has a pH of 3.5 to 6, that does not contain chromium,and that contains a molybdenum compound content of 0.2 to 3.0 weight %calculated as molybdenum and a fluoride content of 0.1 to 2.0 weight %calculated as fluorine.
 2. A process according to claim 1, wherein thepH of the aqueous treatment composition is from 3.8 to 4.5.
 3. A processaccording to claim 2, wherein the molybdenum content of the aqueoustreatment composition is from 0.5 to 2.0 weight %.
 4. A processaccording to claim 1, wherein the molybdenum content of the aqueoustreatment composition is from 0.5 to 2.0 weight %.
 5. A processaccording to claim 4, wherein the fluoride content of the aqueoustreatment composition is from 0.3 to 1.0 weight %.
 6. A processaccording to claim 3, wherein the fluoride content of the aqueoustreatment composition is from 0.3 to 1.0 weight %.
 7. A processaccording to claim 2, wherein the fluoride content of the aqueoustreatment composition is from 0.3 to 1.0 weight %.
 8. A processaccording to claim 1, wherein the fluoride content of the aqueoustreatment composition is from 0.3 to 1.0 weight %.
 9. A processaccording to claim 8, wherein the time of treatment is from 1 to 10seconds and the temperature of the treatment composition duringtreatment is from 30° to 70° C.
 10. A process according to claim 7,wherein the time of treatment is from 2 to 5 seconds and the temperatureof the treatment composition during treatment is from 45° to 60° C. 11.A process according to claim 6, wherein the time of treatment is from 2to 5 seconds and the temperature of the treatment composition duringtreatment is from 45° to 60° C.
 12. A process according to claim 5,wherein the time of treatment is from 2 to 5 seconds and the temperatureof the treatment composition during treatment is from 45° to 60° C. 13.A process according to claim 4, wherein the time of treatment is from 1to 10 seconds and the temperature of the treatment composition duringtreatment is from 30° to 70° C.
 14. A process according to claim 3,wherein the time of treatment is from 2 to 5 seconds and the temperatureof the treatment composition during treatment is from 45° to 60° C. 15.A process according to claim 2, wherein the time of treatment is from 1to 10 seconds and the temperature of the treatment composition duringtreatment is from 30° to 70° C.
 16. A process according to claim 1,wherein the time of treatment is from 1 to 10 seconds and thetemperature of the treatment composition during treatment is from 30° to70° C.
 17. A process according to claim 1, wherein the surface treatedis that of hot-dip zinc-aluminum alloy-plated steel sheet.